Production of polychloroethenes



Patented May 27, 1952 AyIme'r'HenryMaudeand David Solomon Rosenberg,iNia-g'ara Falls; N. Y., 'assig nors 'to Hooker Elect ooheniicalCompany, NfagaraFalls N. Y

, aausrporatidn df 'New York NoDrawing. {Application December: 23, 1949,

"seem No. 134,868

8 Claims. (Cl. 260- 654) This "invention relates to a continuous processfor making polychloroethenes, particularly perchloroethylene andtrichloroethylen'e, 'bythe re action of pentachloroethaneortetrachloroethane with an aqueous alkaline earth metal hydroxide slurry.

This application is a eontinuation-in part of our copending applicationS. N. 653,420 'filed MarchQ, 1946, now abandoned.

In order that our invention'maybe'more'readily understood, wewill"desc'ribe"our'process as chloroethylene by reaction oftetrachloroetliane with lime slurry in accordance with th'efollo'wingequation:

2C2HzCl4+Ca(OH)e-iZCiI-ICls-FZI-IiO-l-CtiClz Prior to ourinventiontrichloroethylene has been made commercially by reaction oftetrachloroethane with an=aqueous suspension of-lime in a batch process.In'orderto obtain as complete a reaction as possible in this process, itis necessary to maintain the calcium hydroxide in the form of asuspension, as by vigorous agitation. This reaction is accompanied byviolent foaming. Any attempt'to'c'ontrol this foaming by graduallyintroducing one reagent into the other has not'been'successful.Consequently, it has been necessary to uselarge reuitors'only. partiallyfilled with reactants, "so "as "to provide adequate space fordisintegration of the "foam. This has resulted 'in'a condition whichgreatly favors the corrosion of the "reactors employed because ofthesevere"corrosiveactionof chlorinated hydrocarbons on the usualferrous metals of construction when associated "witnmoi'sture. Adisadvantage of using such largareactors has been a low yield of producter-unirvomme of reactor space. A further "disadvantaged the batchprocess is thatyduring the'distillation of the crude trichloroethylenefrom the reaction mixture, additional-foaming is agai'nenc'ountered,thus necessitating still further expensive voluminous equipment.

It is, therefore, an object ofjthis invention to provide a continuous"process for the dehydrochlorination of polychloroethanes byfre'actionwith an aqueous alkaline earth hydroxideslurry. A further object is "toprovide an economical process for the production-of triehloroethylene orperchlproethylene which is 5 readily adaptable tocommercialscalemanufacture. An additional object is "to provide aprocess whi'emgivesa high yield of product perumt volume'ofireaetorspace employed. -'A :princi-p'al object is to 'provme a process for t-he-'manui'actu1'e of trichloroethylene uct'per unit'volum'e of reactorspace per unit'of time. A further-object is'to providea process which=eliminates-excessive corrosion of the r'e'actors employed. S-till otherobjects'wilhbecome apparent hereinafter to th'ose" skilledin the-art.

We have now found "that in th'e dehydrochlorination of ahydrogen-containing 'p'olychlo'roethane by reaction with anaqueousalkalirieearth metal hydroxide slurry, the aforesaid and: relatedobjects may be accomplished by-continuously introducing the'polychloroetha'n'e a'n'd aqueous alkaline earth metal hydroxide "slurryinto a closed chamber substantially completely filled with an agitatedbodyo'f the liquid reactionmixture, while maintaining said mixture at atemperature below the boiling "point of any of the organic azeotr'opestherein 'form'ed, continually transferring reaction mixture from saidfirst chamber to asecond chamber containing'aqueous inorganicconstituents of the reaction mixture maintained at a temperatureabovefthe boiling point of the organic azeotropes in the reactionmixture. I

This invention includes two critical steps, (1 maintaining the reactionvessel substantially completely 'filled'with an alkaline liquid reactionmixture, and (2) continually flash distilling 'organic constituents ofthe reaction'mixtu'refrom an aqueous medium comprising the inorganicconstituents thereof maintained at atemperature above the boiling pointof any 'organic'azeotropes therein.

In'the production of trichloroethylene, tetrachloroethane'an'dlimeslu'rry containing between about 2%; and'25 per cent offcalciumhydroxide in water, in between 5 and "50 per cent molar excess over thattheoretically requiredfare continuously introduced into the bottom of aclosed vessel. This vessel is maintained substantially completely filledwith'a vigorously agitated body of the liquid reaction mixture at atemperature below about 72 degrees 'centig'rade, which temperature isbelow the boiling point or tri'chloroethylene-in water (73 degreescentigrade). The reaction is exothermic, however, additional heat tomaintain the reaction temperature above about degrees centigrade andbelow about 72 degrees ce'ntigrade is obtained if necessary byintroducing controlled quantities of livesteam into the'reaction zone.In'order to obtain a-high yield of trichloroethylene, we hav'e foundthat it 'is' only necessary to allow ror a retention time 3 V in thereaction zone of preferably about 25 to 35 minutes.

Liquid reaction mixture is continually with-j drawn from the top of thereaction vessel at a rate equal to the combined rate of introduction ofthe reactants, thus providing for maintaining the reaction vesselsubstantially completely filled 1 with 'liquid reaction mixture; It isimportant about 20 to 40 minutes,

' the bottom section of the vessel through a sparthat withdrawn reactionmixture be continually introduced into a flash distilling vesselpartially filled with the residual aqueous medium comprising theinorganic constituents of the reaction mixture maintained at atemperature between about 94 and 103 degrees centigrade whichtemperature is above the boiling points of the azeo- V tropes oftetrachloroethane or .trichloroethylene,

in water but below the boiling point of the water-l inorganic saltmixture. This manner of distilling on the product is advantageousbecause it prevents the accumulation of organic matter with thelime-containing calcium chloride solution and it assures the practicallycomplete recovery of the organic constituents with the minimum offoaming. The distillation temperature is held at preferably atemperature of about 99 to 101 degrees centigrade, by introducing livesteam into 7 the distillation zone. The 'volatilized chlorinated organicconstituents are continuously removed from the flash distillationchamber, then condensed and separated from any water to recovertrichloroethylene.

j Although this description has been specifically: concerned with thepreparation of trichloroethylene by the dehydrochlorination ofsymmetrical tetrachloroethane using a calcium hydroxide slurry, it is tobe understood that other polychloro hydrocarbon ethanes having theformula .C'zHzCly wherein an is an integer from 1 to 4 inclusive, y isan integer from 2 to 5, inclusive, and the sum of a: and y is 6, mayalso be treated to produce a chloroethene having the formula CZHr-lCly-lwherein a: and y have the above values. Representative ethanes includepentachloroethane, l,1-dichloroethane, 1,2-dichloroethane,;

1,1,2-trichloroethane, 1,1,1-trichloroethane, etc.

Alkaline earth metal'hydroxides other than calcium hydroxide, such asmagnesium hydroxide;

barium hydroxide, etc., may also be used. The temperature ranges givenherein for trichloroethylene are critical. The corresponding temperatureranges for producing other chloroethenes are likewise critical; forexample, the reaction temperature must be maintained below the boilingpointof any of the organic azeotropes therein formed and thedistillation temperature must be maintained at a' temperature abovetheboiling points of the organic azeotropes in the reaction mixture butbelow the boiling point of the residual aqueous medium comprising theinorganic Example I Aclosed reactor provided with an agitator wascompletely filled with a lime slurry containing 5 per cent by weight ofcalcium hydroxide. Forty pounds of about 9 per cent tetrachloroethaneperminute and 235 pounds of 5 per cent by weight calcium hydroxide slurryper minute, representing 20 per cent by weight excess Ca(OI-I)2,

were continuously introduced into the bottom 7 section of the reactionvessel.

of such sizeas to provide for a contact time in the reaction zone ofabout 27 minutes. The re:

The reactor was g er tube. Reaction mixture was continuously withdrawnfrom the reaction vessel at about the combined rate of introducing thereactants, which was 30 gallons per minute; and then continuouslyintroduced into a separate distilling vessel containing aqueous calciumchloride and unreactedlime resulting from the reaction. This aqueousmedium was maintained at a tempera- V ture of about 99 degreescentigrade by introducing live steam thereinto causing an azeotrope oftrichloroethylene and small amounts of tetrachloroethane to'becontinuously flash distilled from the product introduced into the hotmedium. This azeotrope was condensed and about 30 pounds per minute (orabout 2.3 pounds per hour per gallon of reactor space) oftrichloroethylene of about 95 per cent purity was continuously recoveredby gravity separation from the condensed mixture.

Example II In a manner similar to that of Example I, 47 .6 parts byweight per minute of 94 per cent tetrachloroethane and about 300 partsby weight per minute of 5 per cent by weight of calcium hydroxide slurryper minute, representing 47 per cent excess C'a(OI-I)2, werecontinuously introduced into a reaction zone maintained at a temperatureof about 72 degrees centigrade. The

' retention time in the reaction zone was 38 minutes. The reactionmixture was continuously withdrawn from the reactor at the combined rateof introduction of the reactants, and then continuously flash distilledin a separate distilling vessel at a temperature of about 93 degreescentigrade. By condensing the organic'materials, trichloro'ethylene of97.5 per cent purity was recovered at the rate of 34.6 parts by weightper minute.

Example III In the manner of the foregoing examples, about 2 parts byvolume per minute of pentachloroethane and 15 parts by volume per minuteof 5 per cent'by Weight calcium hydroxide slurry representing 20 percentby weight excess Ca(OH)2, were continuously introduced into the ofintroduction of the reactants, and then continuously flash distilled ina separate distilling vessel at a temperature of about 99 degreescentigrade.v By condensing the organic materials, perchloroethylene wascontinuously recovered at the rate of 1.6. parts by volume per minute.

By operating in accordance with our invention, ordinary ferrousmaterials of construction may be used for the reaction vessel, becausecorrosion-thereof due to condensed chlorohydrocarbans in the presence ofmoisture is substantially minimized, by maintaining the vesselsubstantiallycompletely filled and all surfaces bathed with liquidalkaline reaction mixture, thus eliminating the possibility of attack byacid compounds on-the reaction vessel. Our method also provides foreliminating foaming in the reaction vessel, by maintaining itsubstantially completely filled with liquidthus allowing for a maximumyieldper unit volume of reactor space. Also, by

continuously flash distilling off both the product and unreactedpolychloroethane we eliminate a condition which favors foaming; namely,the mixing of substantial quantities of organic compounds with lime andinorganic salts in the presence of water at the temperature ofdistillation and thereby provide for a further saving in the amount ofequipment used for a given volume of production. In the process of ourinvention it is important that the flash distillation be effected at atemperature above the boiling point of any of the organic azeotropes inthe reaction mixture to insure complete recovery of the product and anyunreacted chloroethane.

Various modifications may be made in the method of the present inventionwithout departing from the spirit or scope thereof, and it is to beunderstood that we limit ourselves only as defined in the appendedclaims.

We claim:

1. A continuous process for dehydrochlorinating a polychloroethanehaving the general formula C2H$C1y wherein :1: is an integer from 1 to 4inclusive, 1 is an integer from 2 to 5 inclusive, and the sum of x and yis 6, which comprises: continuously introducing such polychloroethane inthe liquid phase and an aqueous alkaline earth metal hydroxide slurryinto a closed chamber substantially completely filled with an agitatedbody of liquid reaction mixture; maintaining said mixture at a reactiontemperature below the boiling point of any of the organic azeotropestherein formed; continually transferring a portion of thetotal reactionmixture in the liquid phase, at a rate substantially equal to thecombined rate at which the reactants are introduced into the firstchamber, into a second chamber containing aqueous inorganic constituentsof the reaction mixture maintained at a temperature above the boilingpoint of any of the organic azeotropes in the reaction mixture; andcondensing the CQHr-lCly-l and any unreacted polychloroethane compoundso flashdistilled.

2. The process of claim 1 wherein the alkaline earth metal hydroxide iscalcium hydroxide.

3. The process of claim 1 wherein the polychloroethanedehydrochlorinated is pentachloroethane and perchloroethylene isproduced.

4. The process of claim 1 wherein the polychloroethanedehydrochlorinated is tetrachloroethane and trichloroethylene isproduced.

5. The process of claim 4 wherein the alkaline earth metal hydroxide iscalcium hydroxide and. the temperature of the reaction mixture in thefirst chamber is maintained at between 60 to '72 degrees centigrade.

6. The process of claim 5 wherein the rate 6 of transfer of reactionmixture from the first chamber to the second chamber permits a.retention time in the first chamber of between about 20 to 40 minutes.

7. A continuous process for dehydrochlorinating tetrachloroethane toproduce trichloroeth-v ylene which comprises: continuously introducingliquid tetrachloroethane and an excess of aqueous calcium hydroxideslurry into a closedchamber substantially completely filled with anagitated bod of liquid reaction mixture; maintaining said mixture at atemperature of about degrees centigrade; continually transferring aportion of the reaction mixture in the liquid phase, at a ratesubstantially equal to the combined rate at which the reactants areintroduced into the first chamber and which permits a reaction time inthe first chamber of about 20 to 40 minutes, into a second chambercontaining aqueous inorganic constituents of the reaction mixturemaintained at a temperature between about 94 and 103 degrees centigrade;and condensing the trichloroethylene and any unreacted tetrachloroethaneso flash-distilled.

8. A continuous process for dehydrochlorinating pentaohloroethane toproduce perchloroethylene which comprises: continuously introducingliquid pentachloroethane and an excess of aqueous calcium hydroxideslurry into a closed chamber substantially completely filled with anagitated body of liquid reaction mixture; maintaining said mixture at atemperature of about 88 degrees centigrade; continually transferring aportion of the reaction mixture in the liquid phase, at a ratesubstantially equal to the combined rate at which the reactants areintroduced into the first chamber and which permits a reaction time inthe first chamber of about one hour, into a second chamber containingaqueous inorganic constituents of the reaction mixture maintained at atemperature between about 98 and 103 degrees centigrade; and condensingthe perchloroethylene and any unreacted pentachloroethane soflash-distilled.

AYLMER HENRY MAUDE'. DAVID SOLOMON ROSENBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 414,936 Burcey Nov. 12, 18892,369,485 Nichols Feb. 13, 1945 FOREIGN PATENTS Number Country Date171,900 Germany June 18, 1906

1. A CONTINUOUS PROCESS FOR DEHYDROCHLORINATING A POLYCHLOROETHANEHAVING THE GENERAL FORMULA C2HXCLY WHEREIN X IS AN INTEGER FROM 1 TO 4INCLUSIVE, Y IS AN INTEGER FROM 2 TO 5 INCLUSIVE, AND THE SUM OF X AND YIS 6, WHICH COMPRISES: CONTINUOUSLY INTRODUCING SUCH POLYCHLOROETHANE INTHE LIQUID PHASE AND AN AQUEOUS ALKALINE EARTH METAL HYDROXIDE SLURRYINTO A CLOSED CHAMBER SUBSTANTIALLY COMPLETELY FILLED WITH AN AGITATEDBODY OF LIQUID REACTION MIXTURE; MAINTAINING SAID MIXTURE AT A REACTIONTEMPERATURE BELOW THE BOILING POINT OF ANY OF THE ORGANIC AZEOTROPESTHEREIN FORMED; CONTINUALLY TRANSFERRING A PORTION OF THE TOTAL REACTIONMIXTURE IN THE LIQUID PHASE, AT A RATE SUBSTANTIALLY EQUAL TO THECOMBINED RATE AT WHICH THE REACTANTS ARE INTRODUCED INTO THE FIRSTCHAMBER, INTO A SECOND CHAMBER CONTAINING AQUEOUS INORGANIC CONSTITUENTSOF THE REACTION MIXTURE MAINTAINED AT A TEMPERATURE ABOVE THE BOILINGPOINT OF ANY OF THE ORGANIC AZEOTROPES IN THE REACTION MIXTURE; ANDCONDENSING THE C2HX-ICLY-1 AND ANY UNREACTED POLYCHLOROETHANE COMPOUNDSO FLASHDISTILLED.